UC Davis

Attentional selection mechanisms in visual cortex involve changes in oscillatory activity in the EEG alpha band (8-12 Hz), with decreased alpha indicating focal cortical enhancement and increased alpha indicating suppression. This has been observed for spatial selective attention and attention to stimulus features such as color versus motion. We investigated whether attention to objects involves similar alpha-mediated changes in focal cortical excitability. In experiment 1, 20 volunteers (8 males; 12 females) were cued (80% predictive) on a trial-by-trial basis to different objects (faces, scenes, or tools). Support vector machine decoding of alpha power patterns revealed that late (>500 ms latency) in the cue-to-target foreperiod, only EEG alpha differed with the to-be-attended object category. In experiment 2, to eliminate the possibility that decoding of the physical features of cues led to our results, 25 participants (9 males; 16 females) performed a similar task where cues were nonpredictive of the object category. Alpha decoding was now only significant in the early (<200 ms) foreperiod. In experiment 3, to eliminate the possibility that task set differences between the different object categories led to our experiment 1 results, 12 participants (5 males; 7 females) performed a predictive cuing task where the discrimination task for different objects was identical across object categories. The results replicated experiment 1. Together, these findings support the hypothesis that the neural mechanisms of visual selective attention involve focal cortical changes in alpha power not only for simple spatial and feature attention, but also for high-level object attention in humans.SIGNIFICANCE STATEMENT Attention is the cognitive function that enables relevant information to be selected from sensory inputs so it can be processed in the support of goal-directed behavior. Visual attention is widely studied, yet the neural mechanisms underlying the selection of visual information remain unclear. Oscillatory EEG activity in the alpha range (8-12 Hz) of neural populations receptive to target visual stimuli may be part of the mechanism, because alpha is thought to reflect focal neural excitability. Here, we show that alpha-band activity, as measured by scalp EEG from human participants, varies with the specific category of object selected by attention. This finding supports the hypothesis that alpha-band activity is a fundamental component of the neural mechanisms of attention.